Thermodynamics( heat transfer ,due within 3 hours
1. A thin flat plate is positioned in an air flow of 30 m s-1 . The length of the plate in the direction of the flow is 1.0 m. The width of the plate is 0.5 m. The air temperature is 20 oC. The plate temperature is maintained at 80 oC. Determine the heat transfer rate from the plate if: a) the leading edge is smooth (10 marks) b) the leading edge is rough (10 marks) 2. An air duct heater consists of an aligned array of electrical heating elements in which the longitudinal and transverse pitches are SL =25 mm, ST = 25 mm. There are 5 rows of elements in the flow direction (NL = 5) and 4 elements per row (NT = 4). Atmospheric air with an upstream velocity of 10 m s-1 and a temperature of 25°C moves in cross flow over the elements, which have a diameter of 12 mm, a length of 250 mm and they are maintained at a surface temperature of 300°C. Determine: a) the air-side heat transfer coefficient (8 marks) b) the total rate of heat transfer (6 marks) c) the temperature of air leaving the duct heater (6 marks)